This invention relates to fuel cell systems and, more particularly, to multi-stack fuel cell systems.
In building fuel-cell systems, the fuel cells are conventionally stacked one on the other to form a fuel-cell stack. The number of cells determines the power rating of the stack and to provide systems with higher power ratings, a number of fuel-cell stacks are utilized and the outputs of the fuel cell stacks combined to provide the desired power output.
In one type of multi-stack fuel cell system, it has been proposed to modularize the system by forming modular multi-stack fuel cell assemblies each of which contains a plurality of fuel-cell stacks housed within an enclosure. In a system of this design developed for high temperature fuel cell stacks and, in particular, for carbonate fuel cell stacks, a rectangular or box-like containment structure is employed as the enclosure and the stacks are arranged in line along the length of the structure. Each of the stacks within the structure has inlet manifolds for receiving the fuel and oxidant gas needed to operate the stack and outlet manifolds for outputting exhaust fuel and oxidant gases from the stack.
The containment structure includes fuel and oxidant gas inlet ports for communicating through piping or conduits with the respective fuel and oxidant gas inlet manifolds of the stacks. The structure also has fuel and oxidant gas outlet ports for communicating through piping with the oxidant and fuel gas outlet manifolds. The fuel inlet ports are arranged in line along the length of the structure and a header delivers the fuel to each of the ports. A similar type of arrangement is used for the oxidant gas inlet ports. The fuel and oxidant gas outlet ports also communicate with respective headers for carrying the exhaust gases from the modular assembly.
In order to insure an appropriate uniform flow distribution and a desired pressure differential through the stacks, flow baffles are provided in the piping or conduits connecting the fuel and oxidant gas inlet ports to the respective stack inlet manifolds. Each of the stacks and the piping within the enclosure are also insulated to thermally isolate the stacks from the containment structure.
The cold box-like design of the container structure requires thermal expansion joints inside as well as outside of the containment structure to minimize the pressure differential across the fuel and oxidant seals. Nitrogen is also provided to purge any minute leaks from the fuel cell stacks into the enclosure.
While modular multi-stack fuel cell assemblies of the above type performed as desired, the piping and baffle requirements made each assembly complex and expensive. The thermal insulation requirements were also stringent, further adding to the cost of each assembly. Additionally, the need for a nitrogen gas purge added another gas stream increasing the process control requirements. These factors have lead designers to look for less complex and less costly design alternatives.
It is, therefore, an object of the present invention to provide an improved modular multi-stack fuel-cell assembly.
It is a further object of the present invention to provide a modular multi-stack fuel-cell assembly in which stack to stack flow distribution and differential pressure requirements are realized in a simpler and more cost effective manner.
It is yet another object of the present invention to provide a modular multi-stack fuel cell assembly in which input and output port requirements and piping requirements are significantly reduced.
It is a further object of the present invention to provide a modular multi-stack fuel cell assembly in which the manner of insulating the assembly is improved.
It is a further object of the present invention to provide a modular multi-stack fuel cell assembly in which the enclosure of the assembly and the connections to and from the enclosure are simplified.
It is yet an additional object of the present invention to provide a modular multi-stack fuel cell assembly of the above type which eliminates the use of a nitrogen purge, minimizes the thermal insulation and reduces the piping and associated expansion joints.